The interim Ghana soil classification system and its relation with the World Reference Base for Soil Resources
Soil mapping, classification and evaluation began in Ghana in 1946 when the Soil Research Institute was a unit of the then West African Cocoa Research Institute located in the Eastern Region of Ghana. The experience of the first Director, Mr C.F. Charter, with soils of a number of Commonwealth Countries, enabled him and his assistant, Mr H. Brammer, to formulate what is known as the Ghana Interim Soil Classification System. The System has been the basis of classification of soils in many Commonwealth countries where the two and their other colleagues worked.
The System, which is multi-categorical, has been an important tool in the mapping and classification of soils in the whole country. However, with the present advances in soil classification, the System is now found to have gaps. Consequently, the Soil Science Society of Ghana has requested for an upgrade of the System.
This paper describes major soil units mapped under the system and their suitability for agricultural production.
The World Reference Base (WRB) for soil resources is reviewed and its importance highlighted.
A review of the maxic qualifier in Vertisols is suggested. The view for an introduction of vertic qualifier in the Gleysols was expressed. The control section for base saturation and cation exchange capacities for certain soils with Argic horizon are found to pose difficulties in soil mapping and classification.
A correlation exercise is also carried out between observations made on the major soils of Ghana and the major reference groups of the World Reference Base for Soil Resources.
The system recognizes the following categories (levels):
The lowest classification unit operates on what may be termed as the `soil species' concept.
In the Ghana's soil classification system, the factors of soil formation are more central than the concept of diagnostic horizons as contained in the Soil Taxonomy (Soil Survey Staff, 1975), Soil Map of the World Revised Legend (FAO/UNESCO, 1988) and World Reference Base for Soil Resources (ISSS/ISRIC/FAO, 1998). A few individual soil properties are apparently over-emphasized.
There are four orders, namely:
Climatophytic earths
These are well drained soils whose genesis is considered to have been predominantly influenced by climate and vegetation of the areas in which they occur. The suborders are differentiated by the intensity of leaching into:
Topoclimatic earths
This order comprises soils whose formation is due mainly to climate and relief (high mountains). These are apparently absent in Ghana and exist only in theory.
Topohydric earths
The morphological and physico-chemical characteristics of these soils are primarily influenced by the relief and drainage conditions. They have impeded drainage. Five suborders are recognised under this order.
The suborders of the Topohydric earths, except the Depressiopeds, are grouped at soil group family level according to the nature and reaction of the groundwater that influences the soil. The following are recognised: very acid, acid, neutral, calcium and sodium group families. The Depressiopeds are grouped into Gleisols (very acid, acid and neutral) and Vleisols (calcium and sodium). The great soil groups are presented in Table 1.
Lithochronic earths
The development of these soils are mainly influenced by parent material and time over which the soil is developed. The profiles of these soils are generally immature. The specific factors that cause the young nature of the soils are used to group them into suborders.
In order to cover the whole country on a small scale of the order of 1:1 500 000 or smaller, up to 1:3 000 000, the great soil group taxonomic level is adopted. However, soil maps at a scale of 1:250 000 cover the whole country. On these maps, the soils are grouped into Consociations, Associations and Complexes of soil series and described in greater detail. Detailed soil surveys in the country have produced maps at the level of phases of soil series (Agyili et al., 1993, Asiamah et al., 1996).
About 42 great soil groups have been defined in the Interim Ghana soil classification system (Brammer, 1962). Among these the dominant ones are the Forest Ochrosols, Savanna Ochrosols and Forest Oxysols. These are deeply weathered soils belonging to the Latosol soil group family at the preceding higher level. They are similar to the Zonal soils described in the broad soil classification system of Vine (1966), and by Webster and Wilson (1980). Other extensive soils include the Groundwater Laterites, Tropical Black Clays and Tropical Grey Earths.
These are deeply weathered soils found in the semi-deciduous forest and parts of the forest-savanna transition agro-ecological zones of Ghana. These zones stretch from West to East along the middle portions of the country across the Volta Lake. The soil profiles are matured and often show clay accumulation in the subsoil.
They consist of thin (about 20 cm), dark greyish brown, humus-stained, sandy loam and silt loam topsoils which are usually moderate fine granular in structure and friable in consistency. The subsoils are thick, often more than 120 cm thick over the weathered substratum. They may be red or brown to yellowish brown showing faint mottles as influenced by physiography and internal drainage. Coarse and prominent mottles occur in plinthic horizons. The texture of the subsoil is highly variable. It may be sandy clay loam, silty clay loam, sandy clay or silty clay with common to many (10-40%) quartz gravels and stones and hard iron and manganese dioxide concretions. The soils are moderate to strong medium subangular blocky to angular blocky structured with firm to very firm consistence. Non-gravelly, non-concretionary materials of about 50-120 cm thick from the surface may develop in what is locally termed as drift materials on small hills and upland depressions.
Soil colour is an important criterion in grouping these soils at the succeeding lower taxonomic level (Great soil subgroup) under which we have Red and Yellow Forest Ochrosols. These are further subdivided according to parent material and topography with its influence on soil colour (topohydro sequence) into various soil series. On this basis, several soil series have been found and mapped in the semi-deciduous forest belt of Ghana (Ahn, 1961; Adu, 1992). Table 2 shows a summary of the dominant soils on the basis of geology.
The Forest Ochrosols are generally slightly to moderately acid in the topsoil (pH 6.5 - 5.1 in 1:1 soil:water ratio). Moderate to strongly acid soil reactions have been encountered in cultivated sites in this zone in recent studies (Agyili et al., 1992; Dwomo and Asiamah, 1993; Asiamah et al., 2000). These soils are suitable for a wide range of crops especially tree crops such as cocoa, coffee, oil palm, para-rubber, citrus and food crops such as plantain, coco yam, maize, yams and cassava.
The major limitations for sustained agricultural productivity are the moderately steep to steep slopes (8 - 20%) that prevail in the zone. These accelerate soil erosion after the vegetative cover is removed. The soils are also low in nutrients, especially nitrogen and phosphorus, which have organic matter as their primary sources in the traditional agricultural system. Base saturation is often high but cation exchange capacity (CEC) is low, usually above 16 cmol (+)/ kg clay but less than 24 cmol (+)/kg clay. The soils show good responses to fertilizer amendments especially after short fallows.
These are similar to the Forest Ochrosols except that they occur in the savanna areas with semi-arid climatic conditions. Though the soils are moderately deep to deep, the solum is relatively thinner than the forest counterparts. Decomposing rock or hard rock may be encountered within 150 cm depth. The topsoils are generally thin (<20 cm), greyish brown sandy loam, weak granular and friable. The subsoils range from red in summits to brownish yellow middle slope soils (especially on some sandstone soils). Ironstone concretions and sandstone brashes of about 10-40 percent commonly occur in some of these soils. Further differentiation into Red and Yellow Savanna Ochrosols is made at the great soil subgroup level. Several soil series have also been identified in this group of soils. The dominant soil series are presented in Table 2.
The bulk of the country's food crops are grown on these soils. They support crops such as yams, maize, sorghum, millet, cowpea, groundnuts and cassava. Cashew production is currently on the increase on some of these soils where there is enough moisture to support its growth. The main limitations are moisture availability, which is climatic, and nutrient availability. The soils are rather impoverished through continuous cropping/short fallows without nutrient amendments. Erosion hazard is also a serious problem on steep slopes though most parts of the savanna are generally low lying.
These soils occur in the high rainfall forest zone of the country and are restricted to the south-west. Though the soils are commonly found in areas that receive annual rainfall amounts of 1800 mm and above, they have also been found in areas that receive annual rainfall amounts of 1600 mm on certain geologies (parent materials) such as the Tarkwaian quartzites (Brammer, 1962; Dwomo, 1998).
They are similar to the Forest Ochrosols described above in profile morphology. The major differences observed are that the Oxysols are deeply weathered, some to depths of over 4 m (Ahn, 1961). They are paler in colour and mostly orange brown to yellowish brown. In undisturbed areas, the top humus-stained horizons are thinner (<20cm). Organic matter contents are also reported to be relatively lower but more deeply distributed compared with their Ochrosol counterparts (Brammer, 1962). The soils are highly leached. Topsoil pH values which are lower than 5.0 make the soils strongly acid. But the pH usually increases slightly down the profile unlike the Ochrosols, which often show a decreasing trend. In fact, topsoil pH value has been the most distinguishing criterion used to separate these soils where they occur over similar parent materials. This must, however, be used with caution since several other factors could influence soil reaction.
The Forest Oxysols are divided according to subsoil colour into Red and Yellow Forest Oxysols at the great soil subgroup level. The dominant soil series are presented in Table 2.
Though the soils have good physical characteristics, their use for crop production is limited by their strongly acid soil reaction. Only acid tolerant plantation crops such as oil palm, coconut, para-rubber and coffee are grown on these soils. The main food crop is cassava.
These soils are commonly found in the interior savanna zone of northern Ghana. They are mostly associated with Voltaian shales and biotitic complex granites. They occur on gently sloping topography in a plain landscape. They are shallow to moderately deep. The soils are generally pale brown to pale grey sandy loams which contain between 10 to 40 percent ironstone concretions and nodules to depths of about 60 cm. These are abruptly underlain by sheet ironpan, boulders of ironpan or slightly indurated plinthite which grades into weathered mottled bedrock. The Groundwater Laterites are well known for their poor internal drainage conditions that induce temporal water logging conditions during heavy rains. Only a few soil series have been identified in this soil group (Table 2).
Their shallow depths and the abundance of ironstone concretions and nodules, especially those developed over Voltaian shale, limit the agricultural potential of these soils. Rooting volume is reduced and this consequently affects anchorage, nutrient and moisture availability. Extensive waterlogging prevails during the peak of the rainy season thus affecting the availability of oxygen to plant roots. The major crops grown (partly dictated by climate) are maize, sorghum, millet, groundnuts, cowpea and bambara nuts. Wetland rice is locally grown on the low flat terrains which are inundated during the wet season. At such sites, the soils grade into Savanna Lithosols. The Groundwater Laterites developed over granites have relatively deeper and less skeletal solum. They support agriculture better than their shale counterparts (Brammer, 1962; Asiamah et al., 1993a; Senayah et al., 1998).
They are mostly found in the coastal savanna zone (in the Accra-Ho-Keta plains) that stretches along the coast of Ghana up to a few kilometers inland. They are developed over basic gneiss in a generally gentle topography. They are very dark brown to black clays. Weathered gneiss is encountered within 120 cm depth. Most profiles contain calcium carbonate concretions scattered in the subsoil. The profile morphology and topsoil textures are apparently influenced by total amount of rainfall received per annum (Brammer, 1962). The profiles appear deeper and topsoils are lighter (loamy) as the rainfall amounts increase. These soils, apart from their black colour, also crack deep and wide during the dry season. Gilgai micro-relief is very common on the soil surface.
Similar soils developed in local alluvium originating from horneblende granites occur in the Sudan savanna zone of northern Ghana. They are, however, less clayey probably due to the difference in parent material or relatively higher rainfall amounts. Topsoil clay content is usually < 30 percent (Asiamah et al., 1996). These have been grouped as Savanna Gleisols/Tropical Black Clays (Obeng, 1971).
The main limitation of these soils is their workability. They are very heavy and plastic when wet and very hard when dry. They can only be ploughed within a restricted range of soil moisture content that is difficult to attain under rainfed agriculture. Apart from a few thousands of hectares that have been developed for irrigation (for example, Kpong, Asutuare, Afife and Tono irrigation projects) the bulk of these soils are rarely cultivated. Rice and sugar cane are the main crops on the irrigated fields. Small patches of rice fields are also locally cultivated during the wet season. Okro is also cultivated towards the end and beginning of the wet season.
These soils are found in the Accra-Ho-Keta plains in the coastal savanna zone of Ghana. They develop over acidic gneiss and schist, especially on lower slopes where they are locally influenced by drainage. The soils consist of about 30 cm thick of greyish brown, loamy sand or sandy loam, porous topsoil. This is underlain by about 30 cm thick of sodium saturated clay pan (hard pan) which shows polygonal cracking patterns. The surfaces of the prisms show coatings of organic matter. Below the hard pan, the subsoil is yellowish brown slightly and faintly mottled clay with CaCO3 concretions. Often a stone line occurs between the well-developed B-horizon and the underlying weathered rock.
The presence of hardpan within 30 cm depth is a serious physical limitation to root development. The topsoils are naturally low in nutrients and the subsoils which are relatively richer in basic cations are inaccessible to plant roots. These soils are used mostly as open grazing fields.
Other minor great soil groups of taxonomic importance have been mapped in Ghana (Brammer, 1962; Obeng, 1971). These include Forest and Savanna Lithosols, Regosols, Forest and Savanna Gleisols, Groundwater Podsols, Sodium Vleisols and Alluviosols.
They are found both under forest and savanna vegetation. They are shallow or brashy soils developed on steep slopes or have extensive exposures of hard rock and ironpan. They have very little agricultural value.
These are restricted to a narrow strip along the coast of Ghana. They are deep sands developed in a probable coastal dune landscape. The soils are highly acid and poor in nutrients (basically composed of quartz). They are, therefore, generally of low agricultural value. They, however, support good coconut plantations especially in southwestern Ghana where annual rainfall is over 1800 mm. The sandy texture also provides good rooting conditions for extensive root growth of the coconut palm.
They occur along a few of the major river basins (e.g. the Volta, Nasia and Ofin rivers). They occupy terrace positions and are rarely inundated by the present river floods. The soils, due to their alluvial nature, vary in texture, colour and reaction. They are locally used for vegetable and sugar cane production or grazing.
They are developed in old in-filled lagoons locally identified along the coast in the Southwest. The profile consists of about 5 cm of humus-stained sand over about 60 cm of bleached sand that is abruptly underlain by dark brown organic pan. Below the pan the soil is grey to brown sands. Atuabo series is an example of this soil type.
These are saline soils that border the saline coastal lagoons. They stretch eastward from the Songaw lagoon to beyond the Keta lagoon to the Togo border along the Ghanaian coast. They are black to dark grey clays with hard and sticky consistence and well noted for the presence of salt crust on the soil surface, especially on bare lands bordering the margins of the lagoons.
The soils have limited agricultural potential. They are, however, cultivated to sugarcane around the lower Volta basin where they receive an influx of fresh water annually, thereby reducing their sodicity.
These are soils bordering most of the rivers and streams network in the country. They are either recent alluvial deposits or presently influenced by the floods of these drainage channels. The topsoils are usually sandy, loamy or clayey textured and may show buried horizons and lithological discontinuities. Their positions in the flood plains restrict their use for agriculture. They are locally used for wetland rice and sugarcane cultivation. Dry season vegetable gardening is common in some areas.
The system was designed in the late 1950's and early 1960's (Brammer, 1962). Only limited data on the soils of Ghana was available at the time. This could not support a comprehensive soil taxonomic system like such international systems as the Soil Taxonomy (Soil Survey Staff, 1975), FAO (1988); ISSS/ISRIC/FAO (1998). The design of the categorization and pseudo-connotative terminologies in the order and suborders may be commended. The basis of the classification (on the so-called soil forming factors) is, however, weak as revealed in the advancements made in soil science.
Soils are now known to be formed by pedological processes which have recorded in the soil morphological characteristics that may be observed in the field (ISSS/ISRIC/FAO, 1998). The soil forming factors (Jenny, 1941) may influence these processes but are not directly responsible for the development of any soil profile (E. van-Ranst - unpublished lecture notes - University of Ghent, Belgium). Several pedological processes may be active in the soil concurrently , the most active processes leave the most dominant feature(s).
The authors of the above soil classification work, however, need commendation from local soil scientists irrespective of any short falls of the system. Driessen and Dudal (1991) grouped the major soil units of FAO (1988) on similar principles of dominant soil forming factor(s). The demand for taking inventory of the soils of Ghana required that a working legend be adopted. The concept of soil series expressed as the lowest category in the taxonomic system has been very useful.
The soils of Ghana were therefore mapped at a scale of 1:250 000 as Associations, Consociations and Complexes of soil series. Smaller scale soil maps of Ghana are available at the great group level.
The soil series concept is well embraced by local soil scientists. It makes soil mapping rather easy.
Over the years, a few difficulties have been noted through discussions with Ghanaian soil scientists. There are apparently too many soil series because of the framework on which the soil series was defined - mainly by soil forming factors. Any slight difference in adjoining soils resulted in a different name. In fact quite a number of soils have counterpart names or counterpart soil series under different conditions though profile morphology might be very similar. Examples of such are given in Table 3. Some of these soils could be amalgamated into one soil series.
Another problem with our soil series concept is that there was no limit on the extent to which a polypedon may qualify to be a soil series compared to the USDA System (Soil Survey Staff, 1993). There are a lot of soil series which are just localized soils which normally could be inclusions or at most taxadjuncts (Soil Survey Staff, 1993).
Table 3
Examples of soil series and their counterparts under different environmental conditions
Furthermore, the soil series concept requires that people must know the soil and be able to identify such soils. Because most of the people who developed the system and worked with the system have retired long ago, young soil scientists find it difficult to identify soils in the field. This results from the wide range of characteristics of some of the soil series, coupled with changes that occur over time and the representativeness of the reference profile one is using. This necessitates that one may always have to resort to literature and long discussions before a soil series is confirmed.
The increased attention to international soil classification systems has also been to the detriment of a better understanding and improvement of the Interim Ghana soil classification system. Perhaps a little more attention and review could lead to an upgrading of the system.
Since the 1970s nearly all soil series dug, described, sampled and analysed in Ghana by the Soil Research Institute have been classified in at least one international soil classification system, especially the FAO/UNESCO Soil Map of the World Revised Legend (FAO, 1988), the Soil Taxonomy (Soil Survey Staff, 1975; 1992) and the French classification system (ORSTOM). Obeng (1971) also provides generalized correlation on the soils of Ghana at the great soil group level.
Soil correlation in Ghana has generally been progressive without much difficulty on the basis of profile characteristics. Higher categories, for example the great soil groups, also fit in the USDA, FAO and French systems of soil classification. The major soils of Ghana have been correlated with the reference soils of the WRB (Table 4). The main constraints observed are that one soil series may fall into one or two classifications at a given higher categorical level. This is because of the superposition of independently developed systems. For example, Kumasi series may be an Acrisol, Lixisol, or Alisol Reference soils of the WRB. The classification is, therefore, not very consistent and can be confusing. In another instance, the subunit level also imposes difficulty. Kumasi series may have plinthite, many gravels, bright red colour or vertic characteristics. This means the Kumasi series alone is not enough to suggest its agricultural potential and necessary soil management practices.
Depending on the predominant characteristics several subunits may result in most of our soil series.
Another problem in correlating the Interim Ghana Soil Classification System with the WRB and FAO/UNESCO systems is that no provision is made for some characteristics such as vertic at the lower level units. For example, people argue that Gleysols are often under water and do not experience the characteristic wetting and drying conditions required for the formation of Vertisols.
Most of the Black Clays in Ghana, especially Kupela series and sometimes Akuse and Tefle series, show deep and wide cracks and conspicious slickensides but the top 18cm fail to meet the 30% clay content after mixing. This relegates them to the Gleysols and the vertic characteristics forced to the third level. This does not reflect the landuse difficulties associated with these soils. In fact, they "resemble" Vertisols more than Gleysols.
It is suggested that the clay content of Vertisols be reduced or at least a vertic phase for the possible transformation of Gleysols to Vertisols due to climatic and environmental change be introduced.
Some degree of difficulty is also encountered when correlating WRB with the deep soils in Ghana. The control section of base saturation in the Acrisols is within 125cm. That of the Lixisols is throughout the B-horizon which often goes beyond 125cm. Some horizons below 125cm show base saturation of less than 50 percent (NH4Oac). Such soils do not fit into Acrisols or Lixisols.
It has been a common practice that most people classifying soils look up for common diagnostic horizons such as argic horizon and do not go further to look for others that can occur concurrently eg. ferralic horizon. It may be helpful if the limits of ferralic horizon be introduced into the definition of argic horizon stating that lacking the properties that fulfils a ferralic horizon. Scientists may have to take a closer look to avoid any misunderstandings.
Selected soil profiles of the major soils of Ghana are presented below. These are classified in the local, FAO (1988) and WRB (ISSS/ISRIC/FAO, 1998) systems.
Table 4
Soil correlation of the Interim Ghana Soil Classification System with the World Reference Base (WRB)
Ghana classification system Great Soil Groups (Brammer, 1962) |
World Reference Base Reference soils (ISSS/ISRIC/ FAO, 1998) |
Forest Oxysols |
Ferralsols/Acrisols |
Forest Ochrosols |
Acrisols/Alisols/Lixisols Nitisols/Ferralsols/Plinthosols |
Savanna Ochrosols |
Lixisols/Luvisols/Plinthosols |
Groundwater Laterites |
Plinthosols/Planosols |
Tropical Black Clays |
Vertisols (Gleysols) |
Tropical Grey Earths |
Solonetz/Planosols |
Lithosols |
Leptosols/Plinthosols |
Rubrisols |
Lixisols/Luvisols/Plinthosols |
Alluviosols |
Fluvisols |
Gleisols |
Gleysols/Cambisols |
Sodium Vleisols |
Solonchaks |
Regosols |
Regosols/Arenosols |
The present advances in soil sciences require that a universally accepted system of soil classification be introduced. Such a system should replace or at least complement the numerous systems now in operation worldwide. This will enhance improved scientific communication among soil scientists and facilitate technology transfer of soil-based systems. Consequently, agricultural productivity will be enhanced through soil survey activities for sustained food production to feed the evergrowing world population while conserving the environment
Comparisons of the WRB and the local Ghana Classification system show gaps and overlaps which need to be corrected. Normally like the Ghana system, local systems are old and do not incorporate latest findings in soil research. The WRB incorporates latest findings and must therefore be a pivot around which local systems should operate to correct anomalies.
The concept of classifying soils on the basis of morphological properties is laudable since these could be referred from any standard soil profile description. The activity status of such morphological characteristics is, however, essential since they will determine, to some extent, the recommended management practices for the sustained use of any piece of land.
An example of Tropical Black Clays (Source: Asiamah, 1984)
Soil name: |
Tefle series |
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Classification: |
FAO/UNESCO (1988) Eutric Vertisol |
WRB: (1998) Eutri-Pellic Vertisol |
Location: Ho-Keta Plain | |
Parent material: |
Alluvial Clay |
Drainage: Poorly drained |
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Vegetation: |
Fallow farmland/Swamp grass |
Physiography: Flood basin |
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Date: |
13/6/83 |
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Horizon |
Depth (cm) |
Description | ||
Ap1 |
0 - 5 |
Black (10YR 2 /1) moist; clay loam; weak fine granular; slightly sticky, slightly plastic, friable, slightly hard; many fine and medium random tubular pores; pieces of charcoal, many termite burrows and worm casts; many very fine, fine and medium roots; diffused, wavy boundary, pH 4.9. | ||
Ap2 |
5 - 11 |
Very dark grey (10 YR 3/1) moist; clay loam; weak moderate fine and medium granular; slightly sticky, slightly plastic, friable, slightly hard; many fine and medium random tubular pores; pieces of charcoal, many worm burrows and casts; many fine and medium roots; gradual, wavy boundary; pH 4.3. | ||
Ap3 |
11 - 19 |
Very dark grey (10 YR 3/1) moist; clay; moderate fine and medium granular, fine and medium subangular blocky; slightly sticky, slightly plastic; common fine and medium horizontal inped pores; pieces of charcoal, numerous worm casts; and burrows; numerous rusted dark yellowish brown root channels; abrupt, smooth boundary; pH 4.3. | ||
Bg1 |
19 - 30 |
Dark grey (10YR 4/1) moist, common fine distinct clear reddish brown (5YR 4/4) mottles; clay; strong medium subangular blocky; sticky and plastic, firm , hard; continuous thin clay cutans on ped faces, slickensides; few fine and medium horizontal exped pores; common fine and medium roots; clear, wavy boundary; pH 4.2. | ||
Bg2 |
30 - 50 |
Dark brown (7.5YR 4/4) moist; common medium distinct clear brown (7.5YR 5/2) mottles; clay; medium and coarse angular blocky; sticky and plastic; very firm, strong; few medium vertical inped pores; continuous moderately thick clay cutans on ped faces, slickensides on large faces; few fine roots; diffused, wavy boundary; pH 4.5 | ||
Bg3 |
50 - 55 |
Dark grey (10YR 4/1) moist, many coarse distinct yellowish brown (10YR 5/8) mottles; clay; angular blocky and very coarse columnar; plastic and sticky, very firm, hard; continuous thick clay cutans on ped faces, slickensides; few medium roots; diffused, wavy boundary; pH 4.4 | ||
BCr |
55 - 138 |
Grey (10YR 5/1) moist, many coarse prominent clear strong brown (7.5YR 5/8) mottles; clay; very coarse angular blocky and very coarse columnar, sticky and plastic, very firm, very hard, continuous clay cutans on ped faces, slickensides; very few medium roots; clear, wavy boundary; pH 4.0 | ||
2Cr |
138 - 177 |
Dark grey (7.5YR 4/0) moist, few fine distinct diffused strong brown (7.5YR 5/8) mottles; clay; medium and coarse columnar structure, very sticky and plastic, very firm, hard, continuous thin clay cutans on ped faces, many fine vertical inped pores; common very fine and fine roots; abrupt, smooth boundary; pH 4.3 | ||
3Cr |
177 - 193+ |
Brown (7.5 YR 4/2) moist; foul smelling; pH 3.7 | ||
An example of Groundwater Podsol (Source: Ahn, 1961)
Soil name: |
Atuabo |
series |
WRB: 1998 Densic Podzol |
Location: |
Coast of Southwestern Ghana (High Rainfall Zone) |
FAO:1988 Haplic Podzol | |
Horizon |
Depth (cm) |
Description |
A1 |
0 - 8 |
Dark grey (10YR 4/1) slightly humous, very fine sand, single grain and loose. pH 4.9. |
E1 |
8 - 53 |
Light grey (10YR 7/1) very fine sand, single grain and loose. pH 5.0. |
E2 |
53 - 80 |
Light grey to white (10YR 7/1) to 8/1) very fine sand, single grain and loose. pH 6.0. |
Bhsm1 |
80 - 110 |
Light brownish grey (10YR 6/2) fine sand, indurated to form soft organic pan. pH 5.0. |
Bhsm2 |
110 - 130 |
Dark brown (10YR 4/3); massive organic pan. PH 5.0. |
An example of Groundwater laterites (Source: Adu, 1995)
Soil name: |
Kpelesawgu series |
|
FAO: |
Eutric Plinthosol |
Vegetation: Tall grass savanna |
WRB: |
Stagnic Plinthosol |
Location: Tamale-Bolgatanga road-Interior savanna |
Parent material: |
Residual concretionary fine sandy clay loam developed |
|
Drainage: |
Imperfect |
Profile No.: NB 34, Lab. No. B2194 |
over ferruginous crust and clay shale |
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Site: |
Middle of very gentle slope (2-3%) |
Horizon |
Depth (cm) |
Description |
Al |
0 - 10 |
Dark brown (10Y 4/3); humous; fine sandy loam; weak granular; very few iron concretions; many fine, roots; pH 6.6 |
A2 |
10 - 23 |
Dark yellowish brown (10YR 4/4); slighty humous; fine sandy loam; few iron concretions; many fine roots; friable; loose; pH 6.4 |
A3 |
23 - 33 |
Yellowish brown (10YR 5/4); fine sandy loam; friable; slightly loose; abundant iron concretions; very few small pieces of ironpan; many fine roots; pH 5.6 |
Btcs |
33 - 53 |
Yellowish brown (10YR 5/6); slightly mottled strong brown (7.5YR 5/6); sandy clay loam; abundant iron concretions, abundant Mn02 stained small pieces of ironpan; few fine roots; very firm; abrupt boundary ; pH 5.6. |
Bsm |
53 - 120 |
Mn02 stained ironpan; massive. |
Bv |
120 - 165 |
MnO2 stained soft ironpan; clay loam; massive; abrupt boundary. |
Btcg |
165 - 205 |
Reddish yellow (7.5YR 6/6) mottled light grey (2.5YR 7/2) and red (2.5YR 4/8); silty clay; massive; very firm; abundant Mn02 stained small pieces of ironpan; abundant iron concretions; few ferruginized rock brash; pH 5.4. |
BC |
205 - 232 |
Yellowish red (5YR 5/6) mottled light grey (2.5YR 7/2), red (2.5YR 4/8) and reddish yellow (7.5 6/8) clay; medium subangular blocky; firm decomposed shale; very few iron concretions; very few ferruginized rock brash; pH 4.8. |
Cr |
232 - 260 |
Mottled light grey (5Y 7/2) brownish yellow (10YR 6/8) and red (2.5YR 4/6); clay; decomposing clay shale; very few Mn02 stains; massive; Very firm; pH 4. |
An example of Savanna Ochrosol (Source: Asiamah et al., 1993b)
General Information |
Soil name: Damongo series |
Classification: |
FAO (1988): Haplic Lixisol |
WRB (1998): |
Chromic Lixisol |
Date of Examination: December 1, 1992 |
Location: Transitional zone |
Physiographic position: |
Upper slope |
Surrounding landform: Undulating |
Drainage: Well drained |
Slope on which profile is sited: |
Almost level (0- 2%) |
Parent material: Drift material derived from sandstone |
Human influence: Old farm land |
Depth of groundwater table: |
Below profile throughout the year |
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Vegetation: |
Medium grass |
Horizon |
Depth (cm) |
Description |
Ap1 |
0 - 6 |
Brown (7.5YR 4/6) moist and dry; loamy sand; weak fine granular; non plastic, very friable, loose; many very fine, horizontal, tubular pores; common medium, fine and very fine roots; clear, smooth boundary; pH 5.9. |
Ap |
6 - 13 |
Dark reddish brown (5YR 3/4) moist and brown (7.5YR 4/6) dry; loamy sand, weak fine to medium granular; non sticky, non plastic, very friable, loose, many very fine, horizontal, inped tubular pores; krotovinas, common medium, fine and very fine roots; diffuse, smooth boundary; pH 5.7. |
Ap3 |
13 - 19 |
Dark reddish brown (5YR 3/4) moist and brown (7.5YR 4/6) dry; loamy sand; moderate medium and coarse granular; non sticky, non plastic, very friable, loose; many very fine and fine, horizontal, inped tubular pores; krotovinas, few pieces of pottery; common very fine and fine few medium roots; abrupt, smooth boundary; pH 5.6. |
AB |
19-35 |
Reddish brown (5YR 4/8) moist; sandy loam; strong medium subangular blocky breaking into fine subangular blocky; slightly sticky, non plastic, firm; common fine and very fine horizontal, inped pores; krotovinas, few pieces of pottery; few medium and fine roots; clear, smooth boundary; pH 5.4. |
Btl |
35-55 |
Dark reddish brown (2.5YR 3/6) moist; sandy clay loam; moderate medium and coarse subangular blocky; slightly sticky, non plastic, firm; patchy thin cutans in pores and ped faces; common medium and fine horizontal and oblique inped pores; few fine roots; gradual, smooth boundary; pH 5..5. |
Bt2 |
55-85 |
Reddish brown (2.5YR 4/6) moist; sandy clay loam; weak to medium coarse and medium subangular blocky breaking easily into fine aggregates; slightly sticky, non plastic, friable to firm; Patchy thin cutans in pores and ped faces; common medium and fine oblique and horizontal pores; few fine roots; diffuse, smooth boundary; pH5.4. |
Bt3 |
85-108 |
Reddish brown (2.5YR 4/8) moist; sandy loam; weak to moderate medium and fine subangular blocky; slightly sticky, non-plastic, friable, no cutans detected; common medium and fine oblique and horizontal pores; few fine roots; diffuse, smooth boundary; pH5.6. |
Bt4 |
108-139 |
Reddish brown (2.5YR 4/8) moist; sandy loam; weak medium and fine subangular blocky; slightly sticky, non plastic, friable; no cutans detected; common medium and fine oblique and horizontal pores; very few fine roots; merging, smooth boundary; pH 5.6. |
Bt5 |
139-179 |
Reddish brown (2.5YR 4/8) moist; sandy loam; weak fine and very fine subangular blocky; slightly sticky, non-plastic, friable; no cutans detected; common medium and fine oblique and horizontal pores; very few very fine roots; pH 5.7. |
An example of Forest Ochrosol (Asiamah 1999, unpublished Ph.D Thesis)
General information |
Registration and Location |
Date of description: 19/12/ 1997 |
Soil unit: Kumasi series |
Location: Semi-deciduous rain forest |
Parent material: Granite |
WRB: 1998 Plinthic Ferralsol |
FAO (1988): Haplic Ferralsol |
Drainage class: Well drained |
Topo-site: Upper slope |
Landuse: Research plots for arable crops |
Horizon |
Depth (cm) |
Description |
Ap |
0 - 17 |
Very dark greyish brown (10YR 3/2) moist; sandy clay loam; weak fine granular; friable, non sticky, non plastic; many fine interstitial pores; few fine and medium, irregular, hard, ironstone concretions; many fine and medium angular fresh quartz stones; many very fine, common fine and few medium roots; abrupt, smooth boundary; pH 5.1. |
Bsc |
17 - 29 |
Yellowish red (5YR 4/6) moist; sandy clay loam; moderate fine subangular blocky; friable, slightly sticky, slightly plastic; common fine interstitial pores; few medium angular fresh quartz stones and gravels; common fine and medium irregular hard ironstone gravels and concretions; few fine and medium roots, abrupt, smooth boundary; pH 5.0 |
Btsc1 |
29 - 44 |
Yellowish red (5YR 5/6) moist; clay; moderate fine subangular blocky; firm, slightly sticky, slightly plastic; common faint clay cutans on pedfaces; common fine and few medium interstitial pores; few angular fresh quartz stones and gravels; common fine and medium irregular ironstone gravels and concretions; few very fine and fine roots; gradual, smooth boundary; pH 4.6. |
Btsc2 |
44 - 75 |
Reddish yellow (5YR 7/6) moist; clay; moderate fine, subangular blocky; firm, sticky, plastic;common distinct clay cutans within pores and on pedfaces; common fine interstitial pores; very few and few angular fresh quartz stones and gravels; common fine, irregular soft and hard, ironstone gravels and concretions, few very fine and fine roots, clear, smooth boundary; pH 4.2. |
Btcsv1 |
75 - 134 |
Red (2.5YR 5/6) moist, few fine faint clear reddish brown mottles (plinthite material); clay, moderate fine subangular blocky; firm, sticky, plastic; distinct clay cutans within pores and on pedfaces; few fine and common medium interstitial pores; very few fine irregular soft and hard, ironstone gravels and concretions; very few fine angular fresh quartz gravels; very few, very fine and fine roots; diffuse, smooth boundary; pH 4.0. |
Btcsv2 |
134 - 173 |
Red (2.5YR 5/8) moist; common fine distinct clear reddish brown and yellowish brown mottles (plinthite material) clay; moderate fine subangular blocky; firm, sticky, plastic; common distinct clay cutans within pores and on ped faces, few fine interstitial pores, many feldspar and mica flakes; few fine and medium angular fresh quartz stones and gravels; very few, fine, hard, irregular, ironstone fragments and concretions; very few, very fine and fine roots; diffuse, smooth boundary, pH 4.0. |
Btcsv3 |
173 - 200 |
Red (10R 5/8) moist, many medium distinct clear reddish and yellowish brown mottles; (plinthite material); clay; strong coarse subangular blocky; sticky, plastic, firm; common distinct clay cutans on pedfaces; few fine angular fresh quartz gravels; few fine and medium interstitial pores; few mica flakes, very few soft and hard ironstone concretions, pH 3.8. |
An example of Tropical Grey earths (Source: Asiamah, 1990)
Soil name: |
Agawtaw series |
Slope on which profile is sited: Flat (1%) |
Author:Team work |
High Category Classification: |
Parent material: Garnetiferous horneblende acidic gneiss |
Location: Accra Plains | |
FAO (1988): |
Molli-Stagnic Solonetz |
Moisture conditions in profile: Dry throughout |
|
WRB (1998): |
Stagni-Mollic Solonetz |
Drainage: Poorly drained |
|
Date of Examination: 9th November, 1990 |
Depth of groundwater: Below the profile |
||
Land form: |
Physiographic position: On a plain |
Surrounding land form: Almost flat |
Horizon |
Depth (cm) |
Description |
A1 |
0 - 15 |
Dark brown (10YR 3/3) moist and dull yellow brown (10YR 4/3) dry; sandy loam; weak to moderate, medium and fine granular; non sticky, non plastic, loose, soft; common fine and very fine continuous vertical inped tubular pores; many fine and very fine roots; clear, smooth boundary; pH 5.8. |
A2 |
15 - 32 |
Dark (10YR 3/3) moist and dull yellow brown (10YR 4/3) dry few fine faint brown (10YR 4/6) mottles; loamy fine sand; strong coarse and medium prismatic; non sticky, non plastic, friable, hard with vertical cracks; common very fine and fine continuous random inped tubular pores; few fine angular quartz gravels; very few, small soft, irregular, black manganese dioxide concretions; common medium and few fine roots; clear, smooth boundary; pH 6.9. |
Bmg |
32-68/88 |
Greyish yellow brown (10YR 4/2) moist, few fine faint brown (10YR 4/6) mottles; sandy clay loam; massive slightly sticky, non plastic, extremely firm, extremely hard with vertical cracks; common fine and medium continuous random tubular pores; few fine angular quartz gravels; many small, hard spherical and irregular, black manganese dioxide concretions and few small, hard spherical dark brown ironstone concretions; few fine roots; continuous massive pan; clear, wavy boundary, pH 6.4 - 7.4 |
CBg |
68/88-89/107 |
Dull yellow (2.5YR 6/3) moist and dry, many fine and medium, distinct bright yellowish brown (10YR 5/8) mottles; sandy clay; non plastic, firm, hard; vertical tubular pores; abundant fine and coarse angular, quartz gravels manganese concretions; clay; massive; slightly sticky, common fine and medium roots; pH 7.1. |
An example of Forest Oxysol (Source: Dwomo, 1998)
Profile No: BATP1 |
Soil name: Juaso series |
Human Influence: Clearing |
WRB (1998): Lixic Ferralsol |
FAO/UNESCO (1988): Haplic Ferralsol |
Location: High Rainfall Forest |
Physiographic position: Upper slope |
Drainage: Well drained |
Surrounding Landform: Upland |
Depth of Water Table: Not encountered |
Slope (site): 12% |
Location: High Rainfall Forest |
Moisture condition in Soil: Moist |
Parent material: In situ weathered product of Tarkwian |
Evidence of Erosion: Rill/Gully Erosion |
Horizon |
Depth (cm) |
Description |
Ap |
0 - 10 |
Yellowish brown (10YR 4/2) moist; sandy loam; weak fine granular; non sticky, non plastic, friable; few medium vertical and horizontal pores; common fine, few medium roots; clear smooth boundary; pH 5.3 |
BA |
10 - 21 |
Brown (7.5YR 4/3) moist; sandy loam; moderate medium subangular blocky; slightly sticky, slightly plastic, firm; few fine tubular pores; few pieces of charcoal; few medium, common fine roots; clear smooth boundary; pH 4.7 |
Bt1 |
21 - 55 |
Strong brown (7.5YR 4/6) moist; sandy clay loam; massive, slightly sticky, slightly plastic, firm; common faint clay cutans on ped surface; abundant rounded and flattish quartz gravels, common medium round and irregular quartz stones; few pieces of charcoal; few coarse, few medium and common fine roots; abrupt smooth boundary; pH 4.2 |
Bt2 |
55 - 94 |
Strong brown (7.5YR 5/6) moist; clay loam; moderate medium subangular blocky; slightly sticky, slightly plastic; firm; faint clay cutans on pedfaces; abundant medium rounded and irregular shaped quartz stones, many medium and many fine quartz gravel; few fine roots; clear smooth boundary; pH 4.2 |
Bt3 |
94 - 140 |
Strong brown (7.5YR 5/8) moist; clay; moderate medium subangular blocky, sticky, plastic, firm; few medium, few fine quartz gravel; very few faint clay cutans on ped surface; few traces of decomposing rock; very few fine roots; clear smooth boundary; pH 3.9 |
C |
140 - 180 |
Reddish yellow (7.5YR 6/6) mottled, common faint distinct red (2.5YR 4/6) moist; clay; weak medium subangular blocky; sticky, plastic, firm; common pieces of decomposing rock; pH 3.9 |
An example of Forest Oxysol (Source: Dwomo, 1998)
Profile No: BATP1 |
Soil name: Juaso series |
Human Influence: Clearing |
WRB (1998): Lixic Ferralsol |
FAO/UNESCO (1988): Haplic Ferralsol |
Location: High Rainfall Forest |
Physiographic position: Upper slope |
Drainage: Well drained |
Surrounding Landform: Upland |
Depth of Water Table: Not encountered |
Slope (site): 12% |
Location: High Rainfall Forest |
Moisture condition in Soil: Moist |
Parent material: In situ weathered product of Tarkwian |
Evidence of Erosion: Rill/Gully Erosion |
Horizon |
Depth (cm) |
Description |
Ap |
0 - 10 |
Yellowish brown (10YR 4/2) moist; sandy loam; weak fine granular; non sticky, non plastic, friable; few medium vertical and horizontal pores; common fine, few medium roots; clear smooth boundary; pH 5.3 |
BA |
10 - 21 |
Brown (7.5YR 4/3) moist; sandy loam; moderate medium subangular blocky; slightly sticky, slightly plastic, firm; few fine tubular pores; few pieces of charcoal; few medium, common fine roots; clear smooth boundary; pH 4.7 |
Bt1 |
21 - 55 |
Strong brown (7.5YR 4/6) moist; sandy clay loam; massive, slightly sticky, slightly plastic, firm; common faint clay cutans on ped surface; abundant rounded and flattish quartz gravels, common medium round and irregular quartz stones; few pieces of charcoal; few coarse, few medium and common fine roots; abrupt smooth boundary; pH 4.2 |
Bt2 |
55 - 94 |
Strong brown (7.5YR 5/6) moist; clay loam; moderate medium subangular blocky; slightly sticky, slightly plastic; firm; faint clay cutans on pedfaces; abundant medium rounded and irregular shaped quartz stones, many medium and many fine quartz gravel; few fine roots; clear smooth boundary; pH 4.2 |
Bt3 |
94 - 140 |
Strong brown (7.5YR 5/8) moist; clay; moderate medium subangular blocky, sticky, plastic, firm; few medium, few fine quartz gravel; very few faint clay cutans on ped surface; few traces of decomposing rock; very few fine roots; clear smooth boundary; pH 3.9 |
C |
140 - 180 |
Reddish yellow (7.5YR 6/6) mottled, common faint distinct red (2.5YR 4/6) moist; clay; weak medium subangular blocky; sticky, plastic, firm; common pieces of decomposing rock; pH 3.9 |
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